In a motorcycle where a single-cylinder engine of a small engine displacement is mounted, an exhaust pipe extends from the engine to a lower side of a crankcase and a catalyst converter is connected with the exhaust pipe at the lower side of the crankcase. Moreover, an outlet of the catalyst converter is connected to an exhaust muffler of a rear portion of the vehicle through another exhaust pipe. The motorcycle having the above-described construction has been disclosed (with reference to JP-A No. 2006-226279, for example).
In this motorcycle, exhaust gas which has a high temperature and is exhausted from the engine is supplied to a catalyst in the catalyst converter before the exhaust gas reaches the exhaust muffler. Therefore, the exhaust gas having a higher temperature is supplied to the catalyst and the temperature of the catalyst can be rapidly raised to an activation temperature, as compared with the case where the catalyst is arranged in the exhaust muffler.
In the vehicle where the single-cylinder engine of the relatively small engine displacement is mounted as described in JP-A No. 2006-226279, the catalyst is small so that the catalyst converter in which the catalyst is stored is also small. Therefore, the ground clearance from the ground to the catalyst converter can be sufficiently ensured even when the catalyst converter is arranged at the lower side of the crankcase.
However, in the vehicle where the engine of a moderate engine displacement is mounted, because the catalyst becomes large to be proportional to the engine displacement, the catalyst converter also becomes large. At the lower side of the crankcase, there is no empty space where the catalyst converter can be arranged to ensure the ground clearance. Therefore, in this kind of vehicle, the catalyst converter with the relatively large capacity cannot be arranged compactly.
Here, it is an object of the present invention to provide a catalyst arrangement construction of a vehicle such as a motorcycle where a compact arrangement is available while a lowest ground clearance can be ensured to address problems of the above-described related art.